Data communications by wireless LAN (WLAN) such as an IEEE802.11 standard are now widely used. Wireless data transmission is conducted, for instance, among personal computers (PCs), PC peripherals such as printers, hard disk drives and broadband rooters, electronic appliances such as facsimiles, refrigerators, standard television sets (SDTVs), high-definition television sets (HDTVs), digital cameras, videorecorders and cell phones, signal-transmitting means used in automobiles or aircrafts in place of wired communications, etc.
There are now pluralities of standards such as IEEE802.11a, IEEE802.11b, IEEE802.11g, IEEE802.11h, etc. for wireless LAN. IEEE802.11a uses a modulation system of orthogonal frequency division multiplexing (OFDM), supporting high-speed data communications at 54 Mbps at maximum in a 5-GHz frequency band. IEEE802.11h is a standard for enabling IEEE802.11a in Europe. IEEE802.11b uses a system of direct sequence spread spectrum (DSSS), supporting high-speed communications at 5.5 Mbps and 11 Mbps in an industrial, scientific and medical (ISM) band of 2.4 GHz freely usable without wireless license. IEEE802.11g uses the OFDM modulation system, supporting high-speed data communications at 54 Mbps at maximum in a 2.4-GHz-band like IEEE802.11b.
Also proposed is an extremely convenient, short-distance wireless standard, Bluetooth™, which uses a 2.4-GHz ISM band like IEEE802.11b and IEEE802.11g and can connect associated electronic appliances without a cable. Bluetooth uses a frequency-hopping system with excellent noise resistance, in which a 2.4-GHz ISM frequency band is divided to pluralities of wireless channels, and each wireless channel is divided to time slots every unit time ( 1/1600 seconds), wireless channels used being changed every time slot.
Wireless LAN used by a small group within a distance of about 50-100 m has as high a data-transmitting speed as several Mbps to several tens of Mbps, consuming the power of about 100 mW. On the other hand, Bluetooth is expected to be used in a relatively narrow area within an electromagnetic-wave-reaching-distance of about 10 m, as in the same compound or building, etc., so that it is designed to consume as small power as about 10 mW with a transmission speed of at most 2 Mbps. Because the wireless LAN and Bluetooth are different in a transmission speed, a transmissible range, etc., they can be included in one communications apparatus for selective use depending on applications. Accordingly, high-frequency circuits and high-frequency communications apparatuses will be explained, with IEEE802.11b and IEEE802.11g of wireless LAN as a first communications system, IEEE802.11a and IEEE802.11h of wireless LAN as a second communications system, and Bluetooth as a third communications system for convenience.
JP2001-24579 A discloses a circuit usable for both wireless LAN (IEEE802.11b and/or IEEE802.11g using 2.4 GHz) and Bluetooth. This circuit comprises, as shown in FIG. 34, a first high-frequency switch circuit (SwA) for switching the connections of a first antenna port (AP1) to a transmitting circuit (WLAN TX) of a first communications system and a second high-frequency switch circuit (SwB), the second high-frequency switch circuit (SwB) for switching the connections of a receiving circuit (WLAN RX) of a first communications system to the first high-frequency switch circuit (SwA) and a third high-frequency switch circuit (SwC), and the third high-frequency switch circuit (SwC) for switching the connections of a second antenna port (AP2) to a transmitting/receiving circuit (BT TX/RX) of a second communications system and the second high-frequency switch circuit (SwB), a second filter (FL2) being disposed between the first high-frequency switch circuit (SwA) and the transmitting circuit (WLAN TX) of the first communications system, and a first filter (FL1) being disposed between the second high-frequency switch circuit (SwB) and the receiving circuit (WLAN RX) of the first communications system.
WO03/092997 A discloses a circuit using IEEE802.11b and/or IEEE802.11g using a 2.4-GHz band of wireless LAN, and IEEE802.11a and/or IEEE802.11h using a 5-GHz band of wireless LAN. This circuit comprises a high-frequency switch circuit for switching the paths of a first antenna port (second antenna port) to transmitting circuits of first and third communications systems and receiving circuits of first and third communications systems; a first diplexer circuit connected to a receiving circuit port of the high-frequency switch circuit for branching a high-frequency signal to the receiving circuit of the first communications system and the receiving circuit of the third communications system depending on the frequency bands of the communications systems; a high-frequency filter and a low-noise amplifier connected to a lower-frequency port of the first diplexer circuit; a high-frequency filter and a low-noise amplifier connected to a higher-frequency port of the first diplexer circuit; a second diplexer circuit connected to a transmitting circuit port of the first high-frequency switch circuit for branching a high-frequency signal to the transmitting circuit of the first communications system and the transmitting circuit of the third communications system depending on the frequency bands of the communications systems; a high-frequency filter and a high-frequency power amplifier connected to a lower-frequency port of the second diplexer circuit; and a high-frequency filter and a high-frequency power amplifier connected to a higher-frequency port of the second diplexer circuit.
JP2003-87023 A discloses a circuit usable for Bluetooth and IEEE802.11a and/or IEEE802.11h using a 5-GHz band of wireless LAN. This circuit comprises, as shown in FIG. 35, a first high-frequency switch circuit 3 for switching the paths of a first antenna 8 to a transmitting circuit 1 of a second system and a diversity switch 4, and the diversity switch 4 for switching the paths of a receiving circuit 2 of the second system to the first high-frequency switch circuit 3 and a first bandpass filter 6 having a passband equal to the frequency band of the second system, the first bandpass filter 6 being disposed between a second multiband antenna 9 and the diversity switch 4, and a second bandpass filter 7 having a passband equal to the frequency band of a third system being disposed between the second multiband antenna 9 and a transmitting/receiving circuit 5 of a third system.
As described above, the circuit usable commonly for IEEE802.11b and/or IEEE802.11g using a 2.4-GHz band of wireless LAN and Bluetooth, the circuit usable commonly for IEEE802.11b and/or IEEE802.11g using a 2.4-GHz band of wireless LAN and IEEE802.11a and/or IEEE802.11h using a 5-GHz band of wireless LAN, and the circuit usable commonly for Bluetooth and IEEE802.11a and/or IEEE802.11h using a 5-GHz band of wireless LAN were proposed, but these circuits are adapted to two communications systems, but not usable for three communications systems including IEEE802.11b and/or IEEE802.11g using a 2.4-GHz band of wireless LAN, Bluetooth, and IEEE802.11a and/or IEEE802.11h using a 5-GHz band of wireless LAN.